OK - still not clear on this? Is it just a matter that you've got so many data points you can't see all the x values? If so, (as far as I know) the limit on how many you'll see will depend on how the available space / number of points / font size for the axis combine. Got 10,000 point & you're not going to see all the axis labels...Or does your 'the x values are not uniformly seperated' remark indicate that you're also trying to get the x axis appropriately scales?
Paddy